UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item The Design, Construction and Testing of a Scour Monitoring System Using Magnetostrictive Materials(2014) Day, Steven Richard; Flatau, Alison B; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A system for the continuous monitoring of scour has been designed, constructed and implemented. The system detects the level of scour by attaching flow to a buried post at known depths, and detecting when individual sensors become unearthed. Two bio-inspired flow sensors were designed and constructed for use on the post. The first, resembling a seal whisker, utilized the magnetostrictive materials Alfenol and Galfenol and was optimized for >0.15m/s flow. The second, resembling seaweed, used a conventional permanent magnet and was optimized for <0.15m/s flow. A small, low powered data acquisition system was designed and constructed to monitor and record the data from the sensors. A total of four scour posts were installed at two different sites; two vertically to monitor conventional scour and two horizontally to monitor lateral riverbed migration. Data from the posts was analyzed and presented and lessons learned were documented.Item Development of a Bio-Inspired Magnetostrictive Flow and Tactile Sensor(2012) Marana, Michael Adam; Flatau, Alison; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A magnetostrictive sensor was designed, constructed, and evaluated for use as flow or tactile sensor. Vibrissa-like beams (whiskers) were cut from sheets of the magnetostrictive iron-gallium alloy, Galfenol. These beams were cantilevered, with the fixed end of the whisker attached to a permanent magnet to provide the whisker with a magnetic bias. The free portion of the whisker was quasi-statically loaded, causing the whisker-like sensor to bend. The bending-induced strain caused the magnetization of the whisker to change, resulting in a changing magnetic field in the area surrounding the whisker. The change in magnetic field was detected by a giant magnetoresistance (GMR) sensor placed in proximity to the whisker. Therefore, the electrical resistance change of the GMR sensor was a function of the bending in the whisker due to external forces. Prototype design was aided using a bidirectionally coupled magnetoelastic model for computer simulation. The prototype was tested and evaluated under tactile loading and low speed flow conditions.Item Characterization and Modeling of the Magnetomechanical Behavior of Iron-Gallium Alloys(2006-08-31) Atulasimha, Jayasimha; Flatau, Alison; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Magnetostrictive Iron-Gallium alloys (Galfenol) demonstrate moderate magnetostriction (~350 ppm) under very low magnetic fields (~100 Oe), have very low hysteresis, high tensile strength (~500 MPa), high Curie temperature (~675°C), are in general machinable, ductile and corrosion resistant. Therefore, they hold great promise in active vibration control, actuation, stress and torque sensing in helicopters, aircrafts and automobiles. To facilitate design of magnetostrictive actuators and sensors using this material, as well as to aid in making it commercially viable, it is necessary to perform a comprehensive characterization and modeling of its magnetomechanical behavior. This dissertation addresses some of these issues, focusing primarily on quasi-static characterization and modeling of the magnetomechanical behavior of single-crystal FeGa alloys with varying gallium content and along different crystallographic directions, and studying the effect of texture on the magnetomechanical behavior of polycrystals. Additionally, improved testing and modeling paradigms for magnetostrictive materials are developed to contribute to a better understanding and prediction of actuation and sensing behavior of FeGa alloys. In particular, the actuation behavior (λ-H and B-H curves) for 19, 24.7 and 29 at. % Ga <100> oriented single crystal FeGa samples are characterized and the strikingly different characteristics are simulated and explained using an energy based model. Actuation and sensing (B-σ and є-σ curves) behavior of <100> oriented 19 at. % Ga and <110> oriented 18 at. % Ga single crystal samples are characterized. It is demonstrated that the sensing behavior can be predicted by the model, using parameters obtained from the actuation behavior. The actuation and sensing behavior of 18.4 at. % Ga polycrystalline FeGa sample is predicted from the volume fraction of grains close to the [100], [110], [210], [310], [111], [211] and [311] orientations (obtained from cross-section texture analysis). The predictions are benchmarked against experimental actuator and sensor characteristics of the polycrystalline sample.Item FEM IMPLEMENTATIONS OF MAGNETOSTRICTIVE-BASED APPLICATIONS(2005-12-14) Benatar, Jonathan Gabriel; Flatau, Alison B; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Magnetostrictive transducers are used in a broad variety of applications that include linear pump drive mechanisms, active noise and vibration control systems and sonar systems. Optimization of their performance relies on accurate modeling of the static and dynamic behavior of magnetostrictive materials. The nonlinearity of some properties of magnetostrictive materials along with eddy current power losses occurring in both the magnetostrictive material and the magnetic circuit of the system makes this task particularly difficult. This thesis presents continuum level, three dimensional, finite element analysis of magnetostrictive-based applications for different operating conditions. The Finite element models (FEMs) are based on boundary value problems which are first introduced in the "differential" form (Chapter 2) and then derived to a "weak" form (Chapter 3) suitable for the implementation on the commercial finite element software, FEMLAB 3.1©. Structural mechanics and electromagnetics BVPs are used to predict the behavior of, respectively, structurally-involved parts and the electromagnetic circuit of a magnetostrictive-based application. In order to capture the magnetostrictive material's behavior, static and dynamic three-dimensional multi-physics BVPs include magneto-mechanical coupling to model magnetostriction and the effect of the magnetic stress tensor, also known as Maxwell stress tensor, and electromagnetic coupling to model eddy current power losses (time-harmonic and dynamic case only). The dynamic formulation is inspired by the finite element formulation in the Galerkin form introduced by Perez-Aparicio and Sosa [1], but focuses on a weak form formulation of the problem suitable for implementation in the commercial finite element software FEMLAB 3.1©. Implementation methods of the introduced models are described in Chapter 4. Finally, examples of these models are presented and, for the coupled magneto-mechanical FEM, compared to experimental results.